85C from this low voltage is very suspicious. I know you said your cooling is less than perfect, but maybe there is something actually wrong with thermal paste or cooler seating?
That would explain poor PBO results.
Overall if you want slower/cooler than stock mode, just turn on ECO mode for 65W operation. Then at least you keep single thread boost.
That's another issue with PBO that I have, I don't even get the single thread boost, which is weird, I understand throttling with all cores at 100%, but one or few cores not even boosting to 4.7 GHz or higher? That can't be right, with ECO mode on, it runs cooler, at 75c max, but effective clocks drops to 2.5 GHz under load, I got terrible single core and multi core score in Cinebench, either I need to tweak PBO more or something's broken, but right now, my main concern is having a functional PC that I can play games on and stream from with the performance I can expect from this CPU, which I get with manual OC.
85c does seem a bit high, but it seems about what I can expect with my current cooler set up + lack of airflow in my case, but I decided to reseat the cooler anyway and flipped the fans so they're both pulling in air from the fan, max temp is now 80c (when benchmarking, gaming at 55c max), idle few degrees cooler, that's an improvement, but like you seemed to suggest, at that voltage, it could be a bit cooler, maybe it's the thermal paste that's the issue, it's Arctic MX-4 that I got like 3 years ago, but they don't really expire, do they? At least not within 3 years of purchasing it, I'm not sure.
Doesn't look like I can do much more to improve the cooling until I get a new case with far better airflow, while I'm here, any suggestions for a better thermal paste (if the one I have is the issue), a new cooler, and a decent fan hub/controller? Something that can fit in a NR200, planning on running 4 fans, 2 at bottom and 2 at top, with air flowing upwards.